Metallurgical techniques have been developed for the manufacture of a metal billet or other object from metal powders created in a predetermined particle size by e.g., microcasting or atomization. Usually highly alloyed with Ni, Cr, Co, and Fe, these powders are consolidated into a dense mass approaching 100 percent theoretical density. The resulting billets have a uniform composition and dense microstructure providing for the manufacture of components having improved toughness, strength, fracture resistance, and thermal expansion coefficients. Such improved properties can be particularly valuable in the fabrication of e.g., rotary components for a turbine where high temperatures and/or high stress conditions exist.
The consolidation of these metal powders into a dense mass typically occurs under high pressures and temperatures in a process referred to as hot isostatic pressing (HIP). Typically, the powders are placed into a container (sometimes referred to as a “can”) that has been sealed and its contents placed under a vacuum. The container is also subjected to an elevated temperature and pressurized on the outside using an inert gas such as e.g., argon to avoid chemical reaction. For example, temperatures as high as 480° C. to 1315° C. and pressures from 51 MPa to 310 MPa or even higher may be applied to process the metal powder. By pressurizing the container that is enclosing the powder, the selected fluid medium (e.g., an inert gas) applies pressure to the powder at all sides and in all directions.
The equipment required for HIP treatment is typically very costly and requires special construction. Due to the extreme temperatures and pressures, the container is substantially deformed or crushed as the volume of the powder decreases during the HIP process and the container becomes joined to the surface of the billet created by the compacted powder. Depending upon the desired shape for the resulting billet, all or portions of the surface of the container may be cut away i.e., by machining after the HIP process. In addition, portions of the billet may also be cut away depending upon the shape desired and the nature of deformations that occurred during the HIP process. Given that the powder used to manufacture the billet is typically very expensive, removal of portions of the billet is undesirable. A process that allows for shape control during compaction while optimizing the removal of material from the billet is needed.
FIGS. 1A and 1B provide an exemplary illustration of the problems confronted using conventional containers in the HIP process. FIG. 1A provides a schematic illustration of a portion of a container 101 before being subjected to the extreme temperature and pressure of the HIP process. Container 101 encloses the powder mixture 105 intended for compaction and provides a seal to prevent the ingress of the fluid used for pressurization e.g., argon during the HIP process. Before pressurization, the walls 110 between top 100 and bottom 135 are basically straight and/or without deformation. Top 100 and bottom 135 are also undeformed before the HIP process.
In general, the thickness, type, and structure of material used for container 101 is determined in part by the weight of powder to be held within container 101. More particularly, in addition to providing a pressure seal, container 101 is also used to transport the powder to a pressure vessel for the HIP process and, therefore, must be constructed to bear the weight of the powder e.g., several tons in some applications. For example, container 101 might be constructed from mild steel of approximately ½″ in thickness. However, other materials and thicknesses may be used. If the container is intended to remain on the billet for inclusion on the ultimate article of manufacture, additional considerations may determine the choice of material for container 101.
FIG. 1B illustrates the same portion of container 101 after being subject to the HIP process. The conditions of the HIP process have now converted the powder into a metal billet 106. However, the change in density from powder to a solid metal has also resulted in a rather dramatic change in volume. As the volume decreased, container 101 also deformed with the change from powder 105 to billet 106. FIG. 1B illustrates that wall 110 has now taken on an arcuate shape, and top 100 and bottom 135 may undergo deformations as well.
Unfortunately, depending upon the shape desired for billet 106 (or the shape of the ultimate component to be constructed from billet 106), the deformations shown in FIG. 1B may be undesirable because the resulting shape for billet 106 may require the removal of valuable material from its surface. For example, assuming a cylindrical outer surface is needed along wall 110 of billet 106, container 101 and billet 106 may need to be cut i.e., machined along line 130 in order to obtain the desired outer surface. However, in addition to the destruction of container 101, significant amounts of the billet 106 will be lost at portions 115 along the top and bottom of container 101. Because of the substantial costs of the original powder, this loss is undesirable. In addition, although less significant than the powder costs, portions of container 101 are also lost as a result of the machining process.
Therefore, an improved device that provides for the reduction or elimination of powder loss in connection with HIP treatment would be useful. An improved device that also allows for more variation in the construction of containers associated with HIP treatment would also be useful.